IMAGES: Deadly Building Collapse

Authorities say Benschop was operating the excavator at the site of a building demolition at 2136 Market Street on the morning of June 5, 2013 when the building's western wall collapsed. The four-story brick wall was free-standing and had not been braced using demolition equipment.

Upgraded Charges for Backhoe Operator in Deadly Building Collapse

Prosecutors upgrated the charges to third-degree murder for the backhoe operator allegedly involved in the Center City building collapse. NBC10's Daralene Jones has the details. (Published Wednesday, Feb 19, 2014)

Benschop was arrested shortly after the collapse and underwent drug and alcohol tests. Police said those tests came up positive for prescription painkiller and marijuana use. Benschop, however, did have a broken arm, for which he said the painkillers were being used.

He and his family have maintained Benschop's innocence during the entire ordeal. His attorney, Daine Grey, told NBC10 Philadelphia in September 2013 that he believed evidence would vindicate his client.

A grand jury investigation, according to Williams, "places Campbell at the center of culpability." Williams said that instead of opting for the safest way to dismantle the building, Campbell opted for the most profitable way, which included salvaging some of the dismantled parts.

Williams said numerous demolition and construction experts testified before the grand jury, explaining that there was one appropriate way to take the building down.

"He therefore chose to maximize his profits by first deciding to remove the joists, which were valuable for his resale." That left the walls without support, Williams said.

On the night before the collapse, Plato Marinakos, an architect and the project's expeditor, allegedly warned Campbell that the unbraced wall could collapse at any time. According to Williams, Campbell promised that night to have the part of the wall that towered above thrift store taken down, brick-by-brick. The work was started, but never finished. On the morning of the collapse, about an hour before the walls crumbled, Campbell called Marinakos and told him the freestanding part of the wall was safely removed.

Marinakos, a key witness for prosecutors in their case against Benschop and Campbell, was granted immunity in exchange for his testimony.

The collapse happened at 10:41 a.m. Four minutes later, Campbell began repeatedly calling Marinakos. When Marinakos arrived on the scene, Campbell admitted to him that the wall wasn't taken down brick by brick, according to the grand jury presentment.

Jay Bryan, the father of Anne Bryan, who was killed in the collapse, told NBC10 he hoped the ongoing grand jury investigation would lead to more results.

"We're grateful that it sounds like the investigation is ongoing," Bryan said. "We hope that everyone will be held accountable from bottom to top."

Pretrial conferences for Benschop and Campbell are set for next month.